Field
The disclosed embodiments relate to power converters for electronic devices. More specifically, the disclosed embodiments relate to techniques for preventing shoot-through in switched-mode power supplies.
Related Art
Flyback converters may be used to convert alternating current (AC) to direct current (DC) in low-power applications such as mobile phone chargers and/or laptop computer power adaptors. For example, an external power supply (e.g., power brick) for a laptop computer may use a flyback converter to convert AC mains power from a power outlet into low-voltage DC that can be used by components in the laptop computer.
During operation of a flyback converter, synchronous rectification (SR) of a secondary metal-oxide-semiconductor field-effect transistor (MOSFET) may be temporarily disabled during light-load conditions to reduce power losses. After the flyback converter exits light-load conditions, active switching of the secondary MOSFET may be enabled by activating an SR controller on the secondary side of the flyback converter. However, the SR controller may activate to an incorrect state by synchronizing with the ringing of the drain to source voltage of the secondary MOSFET instead of a gate-drive signal on the primary side. Such mis-synchronization may increase the amplitude of the ringing and cause the drain-to-source voltage of the secondary MOSFET to drop below a threshold in synchronous rectifier driver for turning on the secondary MOSFET. If the secondary MOSFET is then turned on while the primary MOSFET of the flyback converter is also conducting, a shoot-through of both the primary and secondary FETs may occur in the flyback converter. During the shoot-through, current in the secondary FET may reverse direction and cause the reflected secondary-side current to flow into the primary FET. The sum of the original primary-side current and the reflected secondary-side current may saturate the transformer in the flyback converter and subject the primary FET to both high current and high voltage, which can damage the flyback converter.
Consequently, operation of flyback converters may be facilitated by mechanisms for preventing mis-synchronization-related shoot-through in the flyback converters.